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Vincent H Poor - One of the best experts on this subject based on the ideXlab platform.
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communication under Channel uncertainty an algorithmic perspective and effective construction
IEEE Transactions on Signal Processing, 2020Co-Authors: Holger Boche, Rafael F Schaefer, Vincent H PoorAbstract:The availability and quality of Channel state information heavily influences the performance of wireless communication systems. For Perfect Channel knowledge, optimal signal processing and coding schemes have been well studied and often closed-form solutions are known. On the other hand, the case of imPerfect Channel information is less understood and closed-form characterizations of optimal schemes remain unknown in many cases. This paper approaches this question from a fundamental, algorithmic point of view by studying whether or not such optimal schemes can be constructed algorithmically in principle (without putting any constraints on the computational complexity of such algorithms). To this end, the concepts of compound Channels and averaged Channels are considered as models for Channel uncertainty and block fading and it is shown that, although the compound Channel and averaged Channel themselves are computable Channels, the corresponding capacities are not computable in general, i.e., there exists no algorithm (or Turing machine) that takes the Channel as an input and computes the corresponding capacity. As an implication of this, it is then shown that for such compound Channels, there are no effectively constructible optimal (i.e., capacity-achieving) signal processing and coding schemes possible. This is particularly noteworthy as such schemes must exist (since the capacity is known), but they cannot be effectively, i.e., algorithmically, constructed. Thus, there is a crucial difference between the existence of optimal schemes and their algorithmic constructability. In addition, it is shown that there is no search algorithm that can find the maximal number of messages that can be reliably transmitted for a fixed blocklength. Finally, the case of partial Channel knowledge is studied in which either the transmitter or the receiver have Perfect Channel knowledge while the other part remains uncertain. It is shown that also in the cases of an informed encoder and informed decoder, the capacity remains non-computable in general and, accordingly, optimal signal processing and coding schemes are not effectively constructible.
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power allocation for energy efficiency and secrecy of wireless interference networks
IEEE Transactions on Wireless Communications, 2018Co-Authors: Zhichao Sheng, H D Tuan, Ali A Nasir, Trung Q Duong, Vincent H PoorAbstract:Considering a multi-user interference network with an eavesdropper, this paper aims at the power allocation to optimize the worst secrecy throughput among the network links or the secure energy efficiency in terms of achieved secrecy throughput per Joule under link security requirements. Three scenarios for the access of Channel state information are considered: the Perfect Channel state information; partial Channel state information with Channels from the transmitters to the eavesdropper exponentially distributed; and not Perfectly known Channels between the transmitters and the users with exponentially distributed errors. The paper develops various path-following procedures of low complexity and rapid convergence for the optimal power allocation. Their effectiveness and viability are illustrated through numerical examples. The power allocation schemes are shown to achieve both high secrecy throughput and energy efficiency.
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guiding blind transmitters for k user miso interference relay Channels with imPerfect Channel knowledge
International Symposium on Information Theory, 2016Co-Authors: Wonjae Shin, Vincent H PoorAbstract:This paper proposes a novel multi-antenna relay-aided interference management technique that can use imPerfect Channel knowledge for interference relay Channels. Using the proposed method, it is shown that KM over K+M−1 degrees of freedom (DoF) are achievable in a K-user multiple-input-single-output interference relay Channel when the relay has M antennas with a certain type of limited Channel knowledge. By leveraging this result, it is demonstrated that the interference-free DoF of K are asymptotically achieved as M approaches infinity. One major implication of these results is that even under this limited Channel knowledge, the use of massive antennas at the relay is sufficient to recover the optimal DoF for relay-aided interference networks with Perfect Channel knowledge.
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energy distortion tradeoff with multiple sources and feedback
Information Theory and Applications, 2010Co-Authors: Aman Jain, Vincent H Poor, Deniz Gunduz, Sanjeev R Kulkarni, Sergio VerduAbstract:The energy-distortion tradeoff for lossy transmission of sources over multi-user networks is studied. The energy-distortion function E(D) is defined as the minimum energy required to transmit a source to the receiver within the target distortion D, when there is no restriction on the number of Channel uses per source sample. For point-to-point Channels, E(D) is shown to be equal to the product of the minimum energy per bit Ebmin and the rate-distortion function R(D), indicating the optimality of source-Channel separation in this setting. It is shown that the optimal E(D) can also be achieved by the Schalkwijk-Kailath (SK) scheme, as well as separate coding, in the presence of Perfect Channel output feedback. Then, it is shown that the optimality of separation in terms of E(D) does not extend to multi-user networks. The scenario with two encoders observing correlated Gaussian sources in which the encoders communicate to the receiver over a Gaussian multiple-access Channel (MAC) with Perfect Channel output feedback is studied. First a lower bound on E(D) is provided and compared against two upper bounds achievable by separation and an uncoded SK type scheme, respectively. Even though neither of these achievable schemes meets the lower bound in general, it is shown that their energy requirements lie within a constant gap of E(D) in the low distortion regime, for which the energy requirement grows unbounded. It is shown that the SK based scheme outperforms the separation based scheme in certain scenarios, which establishes the sub-optimality of separation in this multi-user setting.
Giuseppe Caire - One of the best experts on this subject based on the ideXlab platform.
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finite blocklength Channel coding rate under a long term power constraint
International Symposium on Information Theory, 2014Co-Authors: Wei Yang, Giuseppe Caire, Giuseppe DurisiAbstract:This paper investigates the maximal Channel coding rate achievable at a given blocklength $n$ and error probability $\epsilon$, when the codewords are subject to a long-term (i.e., averaged-over-all-codeword) power constraint. The second-order term in the large-n expansion of the maximal Channel coding rate is characterized both for AWGN Channels and for quasi-static fading Channels with Perfect Channel state information at the transmitter and the receiver. It is shown that in both cases the second-order term is proportional to $\sqrt{(\log n)/n}$.
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mimo downlink scheduling with non Perfect Channel state knowledge
Information Theory Workshop, 2009Co-Authors: Hooman Shiranimehr, Giuseppe CaireAbstract:Downlink scheduling schemes are well-known and widely investigated. In the multiuser MIMO (broadcast) case, downlink scheduling in the presence of non-Perfect CSI is only scantly treated. In this paper we provide a general framework within which the problem can be addressed systematically. Then, we focus on the special case of proportional fairness and “hard fairness”, with Gaussian coding and linear beamforming. We find that the naive scheduler that ignores the quality of the Channel state information may be very suboptimal. We propose novel simple schemes that perform very well in practice. Also, we illuminate the key role played by the Channel state prediction error: our schemes treat in a fundamentally different way users with “predictable” or “non-predictable” Channels, and allocate these classes of users over time in a near-optimal fashion.
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mimo downlink scheduling with non Perfect Channel state knowledge
arXiv: Information Theory, 2009Co-Authors: Hooman Shiranimehr, Giuseppe Caire, Michael J NeelyAbstract:Downlink scheduling schemes are well-known and widely investigated under the assumption that the Channel state is Perfectly known to the scheduler. In the multiuser MIMO (broadcast) case, downlink scheduling in the presence of non-Perfect Channel state information (CSI) is only scantly treated. In this paper we provide a general framework that addresses the problem systematically. Also, we illuminate the key role played by the Channel state prediction error: our scheme treats in a fundamentally different way users with small Channel prediction error ("predictable" users) and users with large Channel prediction error ("non-predictable" users), and can be interpreted as a near-optimal opportunistic time-sharing strategy between MIMO downlink beamforming to predictable users and space-time coding to nonpredictable users. Our results, based on a realistic MIMO Channel model used in 3GPP standardization, show that the proposed algorithms can significantly outperform a conventional "mismatched" scheduling scheme that treats the available CSI as if it was Perfect.
Andrea Goldsmith - One of the best experts on this subject based on the ideXlab platform.
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Outage capacities and optimal power allocation for fading multiple-access Channels
IEEE Transactions on Information Theory, 2005Co-Authors: Nihar Jindal, Andrea GoldsmithAbstract:We derive the outage capacity region of an M-user fading multiple-access Channel (MAC) under the assumption that both the transmitters and the receiver have Perfect Channel side information (CSI). The outage capacity region is implicitly obtained by deriving the outage probability region for a given rate vector. Given a required rate and average power constraint for each user, we find a successive decoding strategy and a power allocation policy that achieves points on the boundary of the outage probability region. We discuss the scenario where an outage must be declared simultaneously for all users (common outage) and when outages can be declared individually (individual outage) for each user.
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Capacity and optimal power allocation for fading broadcast Channels with minimum rates
IEEE Transactions on Information Theory, 2003Co-Authors: Nihar Jindal, Andrea GoldsmithAbstract:We derive the capacity region and optimal power allocation scheme for a slowly fading broadcast Channel in which minimum rates must be maintained for each user in all fading states, assuming Perfect Channel state information at the transmitter and at all receivers. We show that the minimum-rate capacity region can be written in terms of the ergodic capacity region of a broadcast Channel with an effective noise determined by the minimum rate requirements. This allows us to characterize the optimal power allocation schemes for minimum-rate capacity in terms of the optimal power allocations schemes that maximize ergodic capacity of the broadcast Channel with effective noise. Numerical results are provided for different fading broadcast Channel models.
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vector mac capacity region with covariance feedback
International Symposium on Information Theory, 2001Co-Authors: Syed A Jafar, Sriram Vishwanath, Andrea GoldsmithAbstract:We analyze the capacity region for the multiple access Channel with multiple transmit and receive antennas. For Rayleigh fading with Perfect Channel state information at the receiver (CSIR) and only a knowledge of the spatial correlations at the transmitter, we determine the optimal transmit strategies to achieve the points on the boundary of the capacity region under various correlation models.
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on optimality of beamforming for multiple antenna systems with imPerfect feedback
International Symposium on Information Theory, 2001Co-Authors: Syed A Jafar, Andrea GoldsmithAbstract:We determine a necessary and sufficient condition under which beamforming (scalar coding) achieves Shannon capacity in a narrowband point to point communication system employing multiple transmit antennas and a single receive antenna. We assume Perfect Channel state information at the receiver (CSIR) and either Channel mean or Channel covariance feedback from the receiver to the transmitter. We find that better feedback quality not only increases the system capacity but also reduces the required decoding complexity at the receiver.
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adaptive modulation over nakagami fading Channels
Wireless Personal Communications, 2000Co-Authors: Mohamedslim Alouini, Andrea GoldsmithAbstract:We first study the capacity of Nakagami multipath fading (NMF) Channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF Channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We then analyze the performance of practical constant-power variable-rate M-QAM schemes over NMF Channels. We obtain closed-form expressions for the outage probability, spectral efficiency and average bit-error-rate (BER) assuming Perfect Channel estimation and negligible time delay between Channel estimation and signal set adaptation. We also analyze the impact of time delay on the BER of adaptive M-QAM.
Luc Vandendorpe - One of the best experts on this subject based on the ideXlab platform.
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outage probability analysis of a mimo relay Channel with orthogonal space time block codes
IEEE Communications Letters, 2008Co-Authors: Batu K Chalise, Luc VandendorpeAbstract:We investigate the performance of a cooperative multiple-input multiple-output (MIMO) relay Channel in which the source and relay use the same orthogonal space-time block code (OSTBC) for transmission whereas the relay and destination use maximum-ratio-combining (MRC) for reception. Considering that Perfect Channel state information is available at the relay and destination, we derive a closed-form expression for the outage probability of the destination signal-to-noise ratio (SNR) in terms of the confluent hypergeometric function of two variables in a Rayleigh flat-fading environment. The validity of the closed-form expression is confirmed with the numerical results.
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a semi analytical method for predicting the performance and convergence behavior of a multiuser turbo equalizer demapper
IEEE Transactions on Signal Processing, 2007Co-Authors: V Ramon, Cedric Herzet, Luc VandendorpeAbstract:This paper proposes a simple semi-analytical method with reduced simulation time for predicting at any iteration the performance of a turbo-equalization/demapping scheme using the Wang and Poor soft-in/soft-out (SISO) minimum mean-square error (MMSE)/interference cancellation (IC) equalizer and a SISO decoder. The proposed method may be applied to multilevel/phase data modulations as well as multiuser context. This paper shows that the equalizer behavior may be very reliably predicted totally by calculations (no simulations are needed) whereas that of the decoder still requires simulations. A comparison between the proposed prediction method and plain simulations of the overall turbo equalization scheme demonstrates that our method accurately determines the system performance at any iteration. Static Channels, long frames, and Perfect Channel knowledge are assumed throughout the paper
Naofal Aldhahir - One of the best experts on this subject based on the ideXlab platform.
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secure space time block coding without transmitter csi
IEEE Wireless Communications Letters, 2014Co-Authors: Trevor Allen, Julian Cheng, Naofal AldhahirAbstract:A new technique is presented for securing a space-time block code in the presence of an eavesdropper without Channel state information (CSI) at the transmitter. Assuming Channel reciprocity between the transmitter and the intended receiver, we use the receive signal strength indicator, which is much easier to estimate reliably than CSI, to randomly rotate the information symbols at each transmit antenna without increasing the transmit signal's peak-to-average ratio. It is shown that the proposed scheme guarantees full diversity to an intended recipient while reducing the diversity order of an eavesdropper to zero even in the presence of Perfect Channel state information.
